The present invention relates to an extrusion die assembly and more particularly to a foam extrusion die assembly of the type disclosed in applicant's U.S. Pat. No. 3,871,812, issued Mar. 18, 1975 and entitled "Foam Extrusion Die".
The design of foam extrusion dies for a profile extrusion line is largely an art, and because the extruded material generally assumes a cross-section different than that of the die orifices, selecting the exact die shape for a desired cross-section is largely a matter of trial and error.
Applicant in his above-noted patent disclosed a foam extrusion die assembly which facilitates obtaining the proper die orifice shape for a desired profile of the extruded product, e.g., foam boards, planks, and logs. Applicant therein provided a die body to which are fastened two spaced, adjustable die lip members having arcuate outer faces which extend axially outwardly from the face of the die body at the discharge end thereof and which together define an elongated, axially outwardly extending, arcuate die orifice through which foaming material moves both laterally and axially outwardly relative to the lip members. The ends of the orifice are each defined by an elongate key which is set in a key way at each side of the die body such that one end of the key is positioned between the lip members. The lip members are mounted on the body portion for slight movement by a plurality of fasteners extending through oversized bores both in the body and lip members and are manipulable such that the die orifice may be opened or closed at the center thereof to correct the shape of the same to obtain readily the desired profile of the extruded product.
Although such type of die assembly has been found to be an improvement over other known types of extrusion dies and die assemblies, no adequate provision is made for continuous positive sealing contact between the lip members and the face of the die body through which material may otherwise pass during operation, and thus may require frequent disassembly and cleaning of the die assembly. Moreover, no provision is made to ensure alignment of the lip members and to prevent lateral movement thereof during operation thus requiring time consuming and frequent adjustments of the lip members. In addition, the minimum die orifice opening at the throat thereof is limited in applicant's prior die assembly by a square key disposed therebetween which may also cause discontinuity in the distribution channel of the die which in turn may disturb and cause stagnation of the liquid flow in the die orifice thus giving the extruded product uneven edges. Also, no provision is made for fluid cooling or heating of the lip members adjacent the orifice during extrusion of material therethrough which oftentimes is critical to control positively the foaming and shaping of the foaming material.